"The older girl let her anger get in the way of good judgment," Fouts wrote, in a Facebook post. "I spoke with a friend of the family and she stated the older girl had apparently posted on social media what she planned on doing to her good friend."

Fouts said anyone who saw the posted threat could perhaps have prevented the killing by telling school officials or law enforcement about it.

"I hope an effort will be made at Fitzgerald HS and other schools to encourage young people to say something if they have knowledge of a potential dangerous conflict," the mayor said, adding: "My heart also goes out to the parents of the young lady who lost her life, as well to the parents of the other girl who now must face a charge of murder! ...Please say something to prevent the unthinkable! See something, say something!"

The alleged stabber and the victim, who has been identified by school officials as Danyna Gibson, were in economics class Wednesday morning when witnesses told police the suspect produced a kitchen knife and stabbed Gibson twice in the chest.

Warren Police Commissioner Bill Dwyer said a school resource officer acted quickly, administering CPR to try to save Gibson, but the teen was pronounced dead at a local hospital.

The suspect, whose name has not yet been released, was arrested at the scene.

There were 20 to 30 other students in the classroom when the stabbing occurred, Dwyer said, and police will be speaking with witnesses as an investigation continues.

Meanwhile, a vigil to remember and honor Gibson is planned for 1 p.m. Thursday on the football field at Fitzgerald High School, where classes were canceled for the day. Superintendent Laurie Fournier said counseling would offered at the school from 8 a.m. until 2 p.m. (A Gofundme page has been set up to raise money for Gibson's family.)

Fouts said that despite this tragedy he believed Fitzgerald is a good school that produces great students. "I have been to many events at Fitzgerald and have always found it to be a community oriented school," the mayor wrote.

The suspect remains in police custody awaiting an arraignment scheduled for Friday. Michigan prosecutes 17-year-olds as adults in homicide cases.

Students anywhere in Michigan can make confidential tips to state authorities through an app, text message, email or the OK2Say website. [Get details here]. Tips are screened by staff at the State Police and shared with schools and local police.